The NSA gets access to the hardware equipment meant for exports, implants its surveillance tools into it and repackages them for export to various countries, writes Glenn Greenwald in his book "No Place to Hide".

Citing a leaked June 2010 report from the head of the NSA’s Access and Target Development department, Greenwald writes: "The NSA routinely receives – or intercepts – routers, servers and other computer network devices being exported from the US before they are delivered to the international customers."

The implanted tools send the signals back to the NSA allowing it to snoop on the devices.

The NSA’s 2010 report, as quoted by Greenwald, says: "In one recent case, after several months a beacon implanted through supply-chain interdiction called back to the NSA covert infrastructure. This call back provided us access to further exploit the device and survey the network."

The US authorities have banned the sale of Chinese manufactured telecoms equipment in the domestic market after complaining about the Chinese Government doing exactly the same.

A report from the US House Intelligence Committee in 2012 accused two Chinese telecom equipment manufacturers Huawei and ZTE of conniving with the state agencies in implanting spy material on the goods meant for exports.

Meanwhile, NSA’s new chief Admiral Mike Rogers said he would take steps to see that the agency was more transparent and candid to public.

In an interview to Reuters CyberSecurity Summit in Washington, Rogers defended NSA’s surveillance programme. He said that some NSA staff were "confused" by the onslaught of criticism because a series of official reviews found that the agency had for the most part abided by US law.